Method for impregnating wood and other materials



Feb. 2, 1937. B. o. HAGER 2,069,491

METHOD FOR IMPREGNATING WOOD AND OTHER MATERIALS Filed March 18, 1955Patented Feb. 2, 1937 UNITED STATES METHOD FOR HVIPREGNATING WOOD ANDOTHER MATERIALS Bror Olo'i Hitger, Stockholm, Sweden, assignor toBolidens Gruvaktiebolag, Stockholm, Sweden, a limited joint-stockcompany of Sweden Application March 18, 1935, Serial No. 11,541

In Sweden ()ctober 8, 1934 '8 Claims.

It is a well-known fact that wood or other organic substances admittingof impregnation can be made resistant to attacks by funguses or othersimilar organisms, e. g. xylophagans, by that the objects are coated orimpregnated with substances having a poisonous action on theseorganisms. The coating methods are economical to use, but the protectiveefiect obtained is very imperfect, which is due to the fact that thepreservative penetrates inside the surface only in a small degree.Themethods of impregnation by means of pressure and vacuum treatmentgive a good distribution of the preservation agents in the objects, butthe processes are always expensive in practical use.

It has been previously proposed to introduce, by double impregnation,difiiculty soluble substances e. g. into wood in such a manner thatfirst a soluble matter is introduced by pressure treatment, the excessbeing removed by putting the objects being treated, under a vacuum,whereupon they are impregnated again, this time with a solution of amatter which gives with the first one a precipitate of a difiicultlysoluble compound. This method is, however, in its execution socomplicated and expensive that it has found but a small use in practice.

The present invention has for its object to avoid these inconveniencesby carrying out the impregnation without pressure treatment, in openvessels, only by the aid of heat. The objects to be preserved, e. g.posts made of wood or the like,

are put down into a bath consisting of a certain solution suitable forthe purpose, which solution is heated to a temperature settled by testsor experiments in eachindividual case. As a result of this heating tothe desired temperature, air is expelled from capillaries and otherhollow spaces in the objects in question and, besides, moisture possiblyoccurring in the objects evaporates and participates in the expulsion.When this process has advanced suniciently far, which for difierentmaterials occurs after periods of time of unequal length, thetemperature of the solution is decreased. On this occasion, part of thewater vapour which has been formed in the hollow spaces, condenseslittle by little so that vacuum arises therein, and, as a result, theimpregnating solution is sucked in. This operation is interrupted when asuitable amount of impregnating solution is taken up by the material,and the objects are then rapidly taken out of this first bath and areimmerged in a second bath or solution. This lattersolution (the fixingsolution) has a lower temperature, so that a further condensation takesplace in the capillaries, with the result that also this second solutionwill be sucked into "the capillaries or the hollow spaces in the objectsin question. This latter solution contains. a matter which with thematter present in the first (oi. zi-sv) (hot) solution formsadifiicultly soluble compound that is fixed in the objects impregnated.

As will be more closely described in the following, it is possible,while applying the same process,

to carry out the method in such a manner that the objects which aregoing to be impregnated with the different solutions, instead of beingmoved from one tank into a second impregnating tank, are permitted toremain in one and the same tank during the two impregnations, the

solution used in the first impregnation, after this first impregnationhas been brought to'an end, being removed from the tank and the second(cool) impregnating solution thereafter being introduced into the same.In practice, the process is conveniently carried out in such a mannerthat, while impregnation with the first solution third tank and theobjects which are contained in the second tank and have been impregnatedto a completion, are taken out and this tank is charged anew, while,after-the impregnation with the first solution in the first tank hasbeen brought to an end, impregnation with the second solution isperformed therein, and so on in succession. According to this form ofthe method the solution used for the first impregnation is drawn offfrom the tank before the second (cool) solution is introduced in thesame tank, and the first solution brought into another tank inwhich thefirst impregnation is to take place, as will be nearer explained withreference to the drawing.

In order further to illustrate the principle of the present inventionthe following example may be given.

Wooden posts are heated in an aqueous solution of sodium arsenate to atemperature immediately below the boiling point (for example, in thevicinity of 100 0.), and are maintained at this temperature during aboutfive hours, whereupon the solution is cooled down to about C. After onehour or so the posts are taken up and are quickly transferred to abathcontaining zinc sulphate, and having a temperature of e. g. 10 to 20 0.,and are left there until they have absorbed the desired amount ofliquid. As a result, zinc arsenate,which is an effective preservativeagainst rot funguses and is not extracted. by water, deposits on thefibres in the posts.

Of course, instead of sodium arsenate an alkaing a metallic ion capableof forming diflicultly soluble metallic arsenite or arsenate may beused. Thus, besides zinc salts soluble salts of barium, calcium andmagnesium and the like are suitable. Also arsenious acid or trioxide ofarsenic may be used in the first (hot) solution, if the second (cool)solution contains such a substance that a difllcultly soluble compoundis formed. For example, arsenious acid or alkaline arsenate gives withalkaline bichromate a precipitate of difiicultly soluble chromearsenate. 0n the whole, all kinds of soluble arsenic compounds whichgive with another soluble substance a difilcultly soluble compound, canbe used.

In the above example it has been stated that certain salts have to beused in the first impregnating solution and other salts in the lattersolution, but the process may, of course, also be carried out in reverseorder.

Instead of or together with one or several of the metallic compoundscontained in the fixing solution and stated above by way of examples,also soluble salts of copper and/or of manganese, e. g. solutions orcopper sulphate or of chloride of copper, of manganese sulphate or ofmanganese chloride or other solutions in connection with said metals andbeing adapted to the purpose may be used.

The following combinations may be stated as examples:

Solutions of or solutions containing:

(A) Copper sulphate and copper chloride (an example of the combinationof salts of the same metal with difierent acids).

(B) Manganese sulphate and zinc chloride (an example of the combinationof salts of different metals and difierent acids).

(C) Calcium chloride and zinc chloride (an example of the combination orsalts of different metals with the same acid).

Also a combination of three or, if desired, a greater number of saltsmay be used. Salts of calcium cannot, however, be used in combinationwith sulphates.

In the following, some examples of individual salts and of combinationsof salts which may be used, are given:

(1) Examples of single salts:

CuS04 CuCh MnSO;

MnCla ZnSOr ZnClz (2) Examples of two salts used together:

In order to reduce the losses of heat in the hot bath when said bathconsists of an aqueous solution, an oil of suitable consistency may bepoured out onto the surface and be allowed to spread thereon. The oilimpedes evaporation, and the heating costs will be considerably reduced.Temperatures and time of treatment as well as the concentration or thesolutions are fixed in each individual case with regard to the nature ofthe objects being impregnated and of the solutions as well as othercircumstances that may exercise an influence upon the desired result.

In a view to further elucidate the method and the manner in which it maybe carried out in practice, two different embodiments of arrangementssuitable for that purpose are shown, by way of examples, in theaccompanying drawing.

Figure 1 shows diagrammatically, in side view, part of the plant, asviewed along the line I-I in Figure 3 in the direction of the arrows.

Figure 2 shows a cross-section through the line IIII in Figure 1.

Figure 3 shows a top plan view of the plant according to Figure 1.

Figures 4, 5, 6 show in similar manner a second embodiment of the plantbeing equipped with three impregnating tanks so arranged that in two ofsaid tanks impregnation may proceed simultaneously, with the first andthe second solution, respectively, while impregnated material is takenout of the third tank and while the same is being loaded with freshmaterial.

The invention will first be described with reference to Figures 1, 2,and 3.

A and B designate the tanks in which the impregnation takes place. 0 andD designate tanks for receiving the difierent solutions by means ofwhich the impregnation is effected. As shown by the drawing, the twotanks A and B are disposed parallel with each other, and the tanks C andD are arranged on a bed i at such a height that liquid can, by gravity,flow from the solution tanks into the difierent tanks A, B through pipes2, 3 provided with shut-off valves 4, 5.

The boiler G (or other heating apparatus suitable for the purpose)communicates with the impregnating tank A, in which impregnation withthe first solution is carried out in such a manner that the solution,through the action of the pump 6, can be brought to circulate from thetank A through the pipe I, the pump 6, the boiler. or other heatingapparatus G and the pipe 8 back to the tank A. Between the pipe 8 andthe pipe 1 there is provided a branching pipe 9 capable of being cut oilby means of a valve l0, and in each of the pipes I and 8, there isprovided a valve II, which valves are so arranged that, if the valve iiis shut off and the valve iii opened, the solution can be brought tocirculate in the manner apparent from the drawing, without passingthrough the boiler G.

I! designates the material to be impregnated.

The method proper is carried out e. g. in the following manner:

Aiter the tank A has been loaded with material l2,whlch is going to beimpregnated, and the tanks C and D have been loaded with the dinerentsolutions (see above) intended for the impregnation and the tank A hasbeen filled with the solution intended for the first impregnation, thislast-mentioned solution is rapidly heated from about 70 C.-whichtemperature it has in the continuation of the work from the precedingimpregnating process "carried out in the same tank-by means of theheater or boiler G which is strongly heated for this purpose. Afterabout an hour or two (the time varies, of course, according to thenature of the material, the capacity of the tank, etc.) and after thetemperature in the tank A has risen to about 95C., the firing, orheating effected otherwise, of the boiler G may be lessened. After 4 to5 hours the circulation through the boiler is out 01f and cool solutionfrom the tank C is allowed to enter, this in order to bring about aslight fall of temperature in the hot solution so that the logs ormaterial in question, in the manner indicated more in detail in thepreceding, will be brought to absorb suitable amount of solution. Theadded amount of solution is as great as the amount absorbed bythe'material being impregnated in each singleaimpregnation operation.

The period of time during which the material has to remain in the tankto absorb a sufficient amount of solution, is dependent on the fall oiftemperature obtained. In order that the cool.- ing shall be as uniformas possible, the solution is brought still to circulate, at this instantnot through the boiler G, however, but whilst passing by said boiler inthe manner indicated above, i. e. by closing the valves ii and openingthe valve it.

When the impregnation of the charge con tained in the tank A has beenterminated, the material is rapidly transferred, by means of suitablelifting or transporting devices, to the tank B, which containsimpregnating solution from the tank D, remaining from a precedingprocess and completed by fresh supply from the tank D, and the materialis allowed to remain in this solution during a period of time adapted tothe purpose, 6. g. about 12 hours, whereupon the material is readyimpregnated and taken out. After the material has been transferred fromthe tank A to B, the tank A is loaded with fresh material (which, afterimpregnation has taken place therein, is then transferred to the tank Bafter the material has been removed from said latter tank.

It ought to be understood that for each new impregnation process newsolution from the tanks C and D must be added to the tanks A andB,respectively, to an amount corresponding to the amount of solutionabsorbed by the amount in the preceding process.

.In order to maintain the material immersed in the solution during thetreatment, it is loaded with weights or locked by means of suitableholding-down devices.

The plant shown in Figures 4, 5, 6 is, in the essentials, similar tothat described above with reference to Figures 1, 2, 3, with thedistinction, however, that three impregnating tanks ESE, H are providedand communicate with the boiler G and the solution tanks C, D in such amanner that, as indicated above, the impregnation with the firstsolution can take place in any of said tanks E, F, H, while at the sametime the impregnation with the second solution takes place in another ofsaid tanks and the taking-out of impregnated material and theintroduction of fresh material can take place in the third tank, inunbroken succession.

For this purpose, the tank C is, via a pipe 3 capable of being cut offby means of a valve 2, connected with a branching pipe which is providedwith branching pipes i5, I6, I"! capable of being cut oif, so that in amanner known per se solution from the tank C can, according to wishes,

, be supplied to any of the tanks E, F, H.

In similar manner, the solution from the tank D may be supplied, via thepipe 2 capable of being cut off by means of the valve l9 andcommunicating with the branching pipe 20 capable of being cut off, toany of said tanks, E, F, H in the manner stated above with relation tothe solution from the tank C. These tanks communicate in turn, via pipes2!, 22, 23 having shut-off valves v 24, with a branching pipe 25 whichin turn, via a pipe 31 capable of being cut off and provided with avalve 26, communicates with the boiler or other heating apparatus G, sothat said boiler can be brought to communicate with any of the tanks H.

From the boiler G extends, in similar manner as above described, a pipeI! provided with a shutofi valve El and a pump 6 and communicating withopposite ends of the tanks E, F, H via the pipe Zll provided withbranching pipes capable of being cut off, so that liquid from any ofsaid tanks can be brought to circulate through the boiler G for thepurpose of being heated.

The pipe 25 is provided with a valve H! which is kept closed when it isdesired that the solution shall circulate through the boiler G, but ifthe valves Ill! and 26 are closed and the valve It! is opened, theboiler will be put out of the circulation, so that the solutionscirculate only through the pump ii and the one of the diiferent tanks E,F, H which, in each individual case, is switched in for the time being.

When the impregnation in one of the tanks, e. g. in E, with the first(hot) solution has been terminated, the material will, according to thisembodiment, not be transferred to one of the other tanks, but theimpregnating solution is instead transferred from the tank E into one ofthe other tanks charged with fresh material-4n the present case, thetank H. The ready impregnated material contained in the tank-E can nowbe removed and fresh material be introduced and the impregnation withthe second cool solution be going on simultaneously in the tank F andthe impregnation with the first hot solution in the tank H as explainedabove.

When the impregnation with the second solution in the tank F and thatwith the first solution in the tank H have been terminated, the solutioncontained in the tank H is conveyed to the tank E and the secondsolutionis conveyed from the tank F to the tank H.

The material in the tank F has now been impregnated to a completion, andthe material can thus be removed from this tank and then fresh materialbe introduced into the same, and so on in succession.

It ought to be understood that fresh solutions are supplied to thedifferent tanks from the tanks C, D is explained above, in order tocause lowering of the temperature when impregnating with the first (hot)solution, and in order to compensate for the solutions consumed duringthe IJI'OCESS.

The impregnating process in itself as regards heating and lowering ofthe temperature in the first tank, where the impregnation with thefirst, hot solution is going on, takes place in the same manner as abovedescribed with reference to Figures l to 3.

In order to bring about this transfer of. solution from one of theimpregnating tanks E, F, H to another there is provided a pumpingarrangement 30 indicated diagrammatically on the drawing, whicharrangement communicates with a pipe 3| forming a continuous circuit andfitted with branching pipes 32, 33, 34 in which are provided valvesadapted to the purpose, so that solutions may, in the manner statedabove, be

transferred from one tank to another in desired sequence. Therealization of the details of such a branching pipe will be evident toall those skilled in the art, so that a special description in thisrespect may be dispensed with.

It ought to be obvious that the tanks A, B, E, I", H and C, D areprovided with suitable means for tapping of! the solutions containedtherein, when required, e. g. at the end of the working.

Having thus described my invention I declare that what I claim is:--

1. A method of impregnating wood with solutions of metallic salts whichcomprises heating the wood to a suiiicient temperature to expel gastherefrom, decreasing the temperature of the wood while in contact witha metallic salt solution thereby sucking solution into the wood,interrupting the sucking action while the wood has capacity to absorbmore solution by separating the wood and solution, and contacting thewood with a second solution of a metallic salt which is capable ofreacting with the firstmentioned salt, said second solution being at alower temperature than the first solution, there- 30 by enabling thesucking action to continue.

2. In the method of claim 1, heating the wood and the first-mentionedsolution to a temperature of approximately 100 C., thereafter decreasingthe temperature of said solution to about 70 to 80 C. and using thesecond solution at a temperature varying from to 20 C.

3. In the method of claim 1, maintaining wood in contact with thefirst-mentioned solution for a period-of about flve hours while at atemperature of approximately 100 C., decreasing the temperature thereofto within the range of about 70 to 80 C., and maintaining thetemperature of the second solution within the range of 10 to 20 C.

4. In the method of claim 1, employing a solution containing an arseniccompound as the first-mentioned solution, and a second solutioncontaining an ion capable of forming a dimcultly-soluble compound witharsenic.

5. In the method of claim 1, applying an oil of suitable consistency tothe surface of the first-mentioned solution. I

6. In the method of claim 1, forming a compound of zinc in the reactionbetween the said salts.

7. In the method of claim '1, forming a compound of copper in thereaction between the said salts.

BRoR OLOF HAGER.

